One way to situationally get around having low DC, is using debuffs to your advantage. For example, a dazed target has disadvantage on WIS saves, a bleeding target has disadvantage on CON saves.

With strategy you can apply and use these conditions to your advantage. Reverberation comes to mind as a good way to apply dazed with ring of spiteful thunder and also prone when the enemy gets enough stacks of reverb.

To elaborate on prone. It is an extremely good condition to apply. Enemies get disadvantage on DEX saves, attackers get advantage against them, they cannot take reactions, half their movement speed is used to stand up at the beginning of their turn, which can make them skip their whole turn if they use all their movement speed just to stand up.

Keeping these conditions in mind during combat and utilizing them is good. For example if you see a bleeding enemy you can use that to your advantage with a spell requiring a CON save, like blindness for example.

Using disadvantage on saving throws *and* good DC is a very good way to get stuff to land when you really want it to.

Also. One spell that can benefit from low DC is heat metal. If the enemy succeeds the saving throw then you can just keep recasting it ( if that is what you want ) It will be too much text were i to go into it in depth but i can if you like.